Working with SQL Server BLOB Data in .NET

Binary Large Objects (BLOBs) are pieces of data that have -usually- exceptionally large size (such as pictures or audio tracks). These values stored in SQL Server in an image column.

Sometimes the term BLOB is also applied to large character data values, such as those stored in text or ntext columns.

Also you can store BLOB data in a binary column, but it doesn’t take larger than 8000 bytes. And image columns are more flexible.

Working with BLOB data is a bit strange because:

You don’t know how much size will be the retrieved data.

The data may be very large so we need to retrieve it in chunks.

Our example is fairly simple. This example stores files in a database (FileStore) and retrieves it by name. The example relies on a database that contains one table, MyFiles. And the table itself contains two columns one for filename (PK) and the other is an image column for the file itself.

Storing BLOB data

Storing BLOB data in a database is easiest part:

In order to run this code, you must add using statements to Sql.Data.SqlClient and System.IO.

Code explanation:First, we created a connection to the SQL Server database. And then, we created the SqlCommand object that will hold the T-SQL Insert statement. After that, we filled the command parameters with required values. Finally, we executed the command.

Well, for avoiding SQL-Injection attacks, it’s recommended that you use parameters instead of hard-coding the argument. Moreover, you can’t represent binary values as strings.
Frankly, it’s recommended using stored procedures instead of coding the commands.

It’s highly recommended that you dispose disposable objects like SqlConnection and SqlCommand. Try encapsulating it in a using statement.

Retrieving BLOB data

Retrieving BLOB data is a bit complex than storing it. The following method demonstrates this:

Code explanation:
After connecting to the database and writing our query, we executed the query by calling ExecuteReader() method of the command object to get read-only forward-only pointer to the retrieved rows.

By default, SqlDataReader reads entire rows -that can be gigabytes of data.- By specifying CommandBehavior.SequentialAccess, it reads the data sequentially in a given chunk size by calling the GetBytes() -or GetChars for BLOB textual data- method.

Calling Read() of the SqlDataReader objects advances the pointer to the next row which is the first single row -if found- in our example.

The GetBytes() method takes five arguments:

The column index.

The index of which to start reading.

The buffer object that will keep current retrieved data.

Index in buffer of which to begin writing t.

The length (chunk size) of the data to retrieve.

It it worth mentioning that this method returns number of bytes retrieved. After calling this method we used a MemoryStream object to write all data retrieved to.

Finally, we retrieve data by calling MemoryStream’s ToArray() function. (I think the code is now clear)

It’s not recommended using MemoryStream if the data is very huge.

SqlConnection, SqlCommand, SqlDataReader, and MemoryStream are all disposable objects.
Because the MemoryStream object may contain the retrieved data it’s highly recommended that you dispose it as soon as possible.

For a complete example download the sample project FileStore.
This project uses a database for storing files and retrieving it.
This database contains only one table, its definition is as follows:

For creating the database, the project also inculdes a SQL Query file that contains the commands for creating it. Simply execute the file.

Like this:

Related

Yeah this is another cool way. However, for data of a big size, it won’t be effective, sometimes it won’t work at all. The way demonstrated in this article works very well under all circumstances and it would be much better in performance compared to other ways.

I’m getting this exception:
System.IndexOutOfRangeException: Index was outside the bounds of the array. at System.Data.SqlClient.SqlDataReader.GetBytes(Int32 i, Int64 dataIndex, Byte[] buffer, Int32 bufferIndex, Int32 length)
at line 18 in the C# code. Anyone have ideas?